1 files changed, 29 insertions, 26 deletions

diff --git a/contrib/llvm-project/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/contrib/llvm-project/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 74664098ce1d..33f122728d2a 100644
--- a/contrib/llvm-project/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/contrib/llvm-project/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1648,8 +1648,32 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
     }
 
   SmallVector<Value *, 4> V1Srcs;
+  // For a recursive phi, that recurses through a contant gep, we can perform
+  // aliasing calculations using the other phi operands with an unknown size to
+  // specify that an unknown number of elements after the initial value are
+  // potentially accessed.
   bool isRecursive = false;
-  if (PV)  {
+  auto CheckForRecPhi = [&](Value *PV) {
+    if (!EnableRecPhiAnalysis)
+      return false;
+    if (GEPOperator *PVGEP = dyn_cast<GEPOperator>(PV)) {
+      // Check whether the incoming value is a GEP that advances the pointer
+      // result of this PHI node (e.g. in a loop). If this is the case, we
+      // would recurse and always get a MayAlias. Handle this case specially
+      // below. We need to ensure that the phi is inbounds and has a constant
+      // positive operand so that we can check for alias with the initial value
+      // and an unknown but positive size.
+      if (PVGEP->getPointerOperand() == PN && PVGEP->isInBounds() &&
+          PVGEP->getNumIndices() == 1 && isa<ConstantInt>(PVGEP->idx_begin()) &&
+          !cast<ConstantInt>(PVGEP->idx_begin())->isNegative()) {
+        isRecursive = true;
+        return true;
+      }
+    }
+    return false;
+  };
+
+  if (PV) {
     // If we have PhiValues then use it to get the underlying phi values.
     const PhiValues::ValueSet &PhiValueSet = PV->getValuesForPhi(PN);
     // If we have more phi values than the search depth then return MayAlias
@@ -1660,19 +1684,8 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
       return MayAlias;
     // Add the values to V1Srcs
     for (Value *PV1 : PhiValueSet) {
-      if (EnableRecPhiAnalysis) {
-        if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) {
-          // Check whether the incoming value is a GEP that advances the pointer
-          // result of this PHI node (e.g. in a loop). If this is the case, we
-          // would recurse and always get a MayAlias. Handle this case specially
-          // below.
-          if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 &&
-              isa<ConstantInt>(PV1GEP->idx_begin())) {
-            isRecursive = true;
-            continue;
-          }
-        }
-      }
+      if (CheckForRecPhi(PV1))
+        continue;
       V1Srcs.push_back(PV1);
     }
   } else {
@@ -1687,18 +1700,8 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
         // and 'n' are the number of PHI sources.
         return MayAlias;
 
-      if (EnableRecPhiAnalysis)
-        if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) {
-          // Check whether the incoming value is a GEP that advances the pointer
-          // result of this PHI node (e.g. in a loop). If this is the case, we
-          // would recurse and always get a MayAlias. Handle this case specially
-          // below.
-          if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 &&
-              isa<ConstantInt>(PV1GEP->idx_begin())) {
-            isRecursive = true;
-            continue;
-          }
-        }
+      if (CheckForRecPhi(PV1))
+        continue;
 
       if (UniqueSrc.insert(PV1).second)
         V1Srcs.push_back(PV1);